Cancer is caused by uncontrolled and unregulated cellular proliferation. Precisely what causes a cell to become malignant and proliferate in an uncontrolled and unregulated manner has been the focus of intense research over recent decades. This research has led to the identification of a number of molecular targets associated with key metabolic pathways that are known to be associated with malignancy.
Heat shock factor 1 (HSF1) is one such target molecule. HSF1 is the master regulator of the heat shock response, in which multiple genes are induced in response to temperature increase and other stresses. At non-shock temperatures in humans and other vertebrates, HSF1 is produced constitutively, but is inactive and bound by protein HSP90. At an elevated temperature, HSF1 is released by HSP90, moves from the cytoplasm to the nucleus, and trimerizes. This active HSF1 form binds to sequences called heat shock elements (HSE) in DNA and activates transcription of heat shock genes by RNA polymerase II. The HSE has a consensus sequence of three repeats of NGAAN and is present in the promoter regions of the HSP90, HSP70 and HSP27 genes. During cessation of the heat shock response, HSF1 is phosphorylated by mitogen-activated protein kinases (MAPKs) and glycogen synthase kinase 3 (GSK3) and returns to an inactive state. The biochemistry of HSFI is described in more detail in, inter alia, Chu et al. 1996 J. Biol. Chem. 271:30847-30857 and Huang et al. 1997 J. Biol. Chem. 272:26009-26016.
HSF1 also interacts with additional factors. For example, HSF1 binds to DNA-dependent protein kinase (DNA-PK), which is involved in DNA repair. HSF1 is also target of mitogen-activated protein kinases, and its activity is down-regulated when the RAS signaling cascade is active.
Additional heat shock factor proteins in humans include HSF2, HSF3, and HSF4. HSF1, HSF2, and HSF3 are all positive regulators of heat shock gene expression, while HSF4 is a negative regulator. HSF1, HSF2 and HSF4 play a role in transcriptional control of other heat shock proteins. The various HSF proteins share about 40% sequence identity.
HSF1 activity has been implicated in several diseases, including cancer, and autoimmune, and viral diseases. HSF1 and other heat shock proteins (whose expression is increased by HSF1) are over-expressed in, or have otherwise been implicated in, breast, endometrial, fibrosarcoma, gastric, kidney, liver, lung, lymphoma, neuroectodermal, neuroblastoma, Ewing's sarcoma, prostate, skin, squamous cell, and testicular cancers, leukemia (e.g., promyelocytic leukemia), and Hodgkin's disease.
Accordingly, there is need for pharmacologically active agents that are capable of inhibiting HSF1. Such agents are potentially useful chemotherapeutic agents for the treatment of diseases or conditions in which HSF1 activity is mediated.